1. Field of the Invention
The present invention relates to acoustic systems.
2. Description of the Prior Art
Conventionally, in a multi-way speaker system using a plurality of combined speakers dedicated for use in a frequency band, for example, have been employed a system where an LC network comprising coils and capacitors or a multi-channel amplifier system where a channel divider dedicated for use in each frequency band (channel) is used. Both the LC network and the channel divider used in multi-channel amplifier systems have such a function that the audible frequency band is divided into some necessary frequency bands and acoustic signals are supplied to the speaker dedicated for use in corresponding frequency bands.
In the multi-channel amplifier system, a digital version of channel divider comprising electronic circuits has been worked out. FIG. 21 is a block diagram which shows one embodiment of channel divider disclosed in the Japanese Utility Model Publication No. 2-6673. FIG. 21 illustrates an example of speaker systems based on the above-mentioned multi-channel amplifier system. In FIG. 21, reference numbers 2, 2.sub.1,2.sub.2, . . . 2n represent a plurality of power amplifiers and 3, 3.sub.1,3.sub.2, . . . 3n represent a plurality of speaker units and also 4 represents a channel divider (frequency band dividing circuit) comprising a plurality of linear-phase FIR type filters 4.sub.1, 4.sub.2, . . . 4n. Reference numbers 4.sub.11, 4.sub.22, . . . 4nn each represent a plurality of filter-factor variable devices which are operating means to give a filter factor in order to give a desired frequency-band dividing characteristics to the above-mentioned linear-phase FIR type filters. Reference numbers 5, 5.sub.1, 5.sub.2, . . . 5n represent a plurality of D/A converters.
In the above-mentioned multi-way speaker system, digital signal inputs are applied to the channel divider 4, in which those input signals undergo convolution operations with the filter factor of the filter factor variable devices 4.sub.11, 4.sub.22, . . . 4nn by the linear phase FIR type filters 4.sub.1, 4.sub.2, . . . 4nn, so that the system may be given desired frequency band dividing characteristics. Next, the outputs of the linear phase FIR type filters 4, 4.sub.1, 4.sub.2, . . . 4n are each converted into analog signals at the corresponding D/A converters 5, 5.sub.1, 5.sub.2, . . . 5n. Those analog signals are then amplified to a predetermined level at the power amplifiers 2, 2.sub.1, 2.sub.2, . . . 2n, so that they can be converted to sounds at the speaker units 3, 3.sub.1, 3.sub.2, . . . 3n.
As described above, since the multi-way speaker system uses the linear-phase FIR type filters 4, 4.sub.1, 4.sub.2, . . . 4n, the sound pressure frequency characteristics of the speaker unit generally do not have linear phases although the linear-phase characteristics are held at the channel divider stage, so that the sound pressure characteristics obtained finally may not always be of linear phases. As a result, the waveforms of reproduced sounds are distorted, which makes it difficult to reproduce the sounds with fidelity.